Aerodynamic and aero-acoustic design of continuous transonic wind tunnel compressor

The continuous transonic wind tunnel, which is generally a closed-circuit variable-density wind tunnel, is an excellent platform for aerodynamic mechanism research and advanced aero vehicles development. A cost-effective and stable continuous transonic wind tunnel requires its driver, usually a multistage axial-flow compressor, to have wide operating range with high adiabatic efficiency and sufficient surge margin. On the other hand, the good test section flow quality requires the outlet and inlet aero-acoustic noise of the compressor lower than 140 dB. Developing a multi-stage axial-flow compressor with high adiabatic efficiency, sufficient surge margin and low noise level working under extra-wide operating conditions faces many challenges. Thus, the effectiveness of the variable geometry method, including variable rotor blade and variable stator vanes, the choice of design point and its corresponding load coefficient and flow coefficient, and the choice of meridional type and the basic principles related to low-noise axial-flow compressor design, were analyzed for the purpose of providing some guidance for designing such a compressor. For compressors with the reaction degree higher than 0.5, the variable rotor blade is more effective. For compressors with the reaction degree lower than 0.5, the variable stator vanes method is more effective than variable rotor blade method. For wind tunnels with operating range from Ma=0.2–1.6, the design point of the compressor should be around Ma=1.4 and its corresponding loading coefficient and flow coefficient are about 0.6 and 0.25 respectively. The constant tip radius meridional type has advantages in aerodynamic performance improvement. Larger rotor-stator spacing and appropriate rotor/stator number ratio are effective in suppressing the compressor noise emission.